fixup lemma 2.6.1 title

Co-Authored-By: KtorZ <[email protected]>

test/unit/Cardano/Wallet/PrimitiveSpec.hs

@@ -76,7 +76,7 @@ spec = do
             (checkCoverage prop_2_1_9)
 
     describe "Lemma 2.6 - Properties of balance" $ do
-        it "2.6.1) dom u ⋂ dom v ==> balance (u ⋃ v) = balance u + balance v"
+        it "2.6.1) dom u ⋂ dom v = ø ==> balance (u ⋃ v) = balance u + balance v"
             (checkCoverage prop_2_6_1)
         it "2.6.2) balance (ins⋪ u) = balance u - balance (ins⊲ u)"
             (checkCoverage prop_2_6_2)